Integrated circuits, hybrid devices and packaging interconnects are all increasing in size and complexity. Large area devices and substrates with high I/O pin counts are becoming more common. One problem with large devices is that it is becoming more difficult to electrically test the circuits. As the density and number of I/O on a circuit increase, conventional probe cards become more difficult to construct and maintain. For large ASIC devices, the number of I/O pads may exceed the maximum density of probes which can be accommodated on a conventional probe card. With some applications, such as probing hybrid substrates or packaging interconnects, an area array of probe locations would be desirable, but impossible to test with current technology. In addition to these problems of probe card complexity, the cost of a probe card increases dramatically as the probe count increases.
Standard electrical probing methods for semiconductor devices utilize needle or "blade" probe cards to provide electrical contact between the test system and the device. Tungsten needles are soldered onto an epoxy board around the perimeter of a hole cut in the probe card. The fabrication of these probe cards is more of an art than a manufacturing technique in that each probe point must be individually soldered to the card, and carefully aligned to a test pad on the device. The planarity and relative position of the needle tips are critical to successful probing of a device. During use, each contact of the probe tips to the test pads causes the needles to be slightly deformed, eventually resulting in the probe card needing repair. This labor intensive method of making and maintaining probe cards causes the price of the card to be high, increasing in cost as the number of probe tips increase.
More recently, membrane probe cards have been proposed, such as those appearing in U.S. Pat. Nos. 4,758,785; 4,891,585; 4,906,920; and 4,918,383. However, these proposals have not found widespread acceptance, due to lack of reliable contact with the chip pads, and excessive cost.